1. Field of the Invention
This invention relates in general to methods and devices for monitoring the corrosive effects of fluids in a producing well, and in particular to methods and devices for monitoring corrosive effects of well fluids by installing a monitoring device downhole in a side pocket mandrel.
2. Description of the Prior Art
Wells such as those used for the production of oil or gas normally contain several concentric metal conduits extending from the bottom of the well to the surface. The inner conduits are known as well tubing and the outermost conduit is known as the well casing. Various fluids flow or are pumped upwardly or downwardly within the innermost tubing or within the annular spaces between conduits.
One or more of these fluids may be highly corrosive to the steel conduits. Carbon dioxide and hydrogen sulfide are common corrosives in many oil and gas wells. Tubing or casing failure because of corrosion necessitates extensive workover. In order to combat corrosion, various chemicals are injected into the well or into the producing formation. These chemicals inhibit the corrosive action of the well fluids on the steel tubing and casing.
The injection of corrosion inhibitor into a well has at times been unsuccessful because of the failure of the solution to completely coat the metal to be protected. U.S. Pat. No. 3,385,358 (Shell) shows a monitoring device used to inspect for total coverage. A tracer material is included in the inhibitor solution prior to injection. Then, after injection, a radioactivity detector is lowered into the well on a wireline to monitor the coverage of the inhibitor solution.
Another method of monitoring the effects of corrosion inhibitor is to insert metal coupons into the fluid for a specified time and then inspect the coupons. One method and apparatus for inserting coupons into a surface pipeline is described in U.S. Pat. No. 4,275,592 (Atwood). This method is excellent for monitoring fluid in a surface pipeline, but the corrosive effects of the fluid in the surface pipeline may be different from the corrosive effects of fluid downhole.
Corrosion monitoring coupons have been placed downhole in devices which are lowered down the string of tubing. The device then locks in place within the tubing. Since the test device is in the tubing, the device partially blocks the flow of fluid through the tubing, and the device must be removed before other tools can be run down the tubing.